HEIDENHAIN TNC 426 (280 476) - Manual (Page 161)

134 6 Programming: Programming Contours
6.3 Cont
our Appr
oac
h and Depar
tur
e n End point P
N
The position P
N
lies outside of the contour and results from your
input in the DEP block. If the DEP block also contains a Z axis
coordinate, the TNC will first move the tool to P
H
in the working
plane, and then move it to the entered depth in the tool axis.
You can enter the position data in absolute or incremental coordinates
and in Cartesian or polar coordinates.
The TNC does not check whether the programmed contour will be
damaged when moving from the actual position to the auxiliary point
P
H
. Use the test graphics to simulate approach and departure before
executing the part program.
When approaching the contour, allow sufficient distance between the
starting point P
S
and the first contour point P
A
to assure that the TNC
will reach the programmed feed rate for machining.
The TNC moves the tool from the actual position to the auxiliary point
P
H
at the feed rate that was last programmed.
Radius compensation
The tool radius compensation is programmed together with the first
contour point P
A
in the APPR block. The DEP blocks automatically
remove the tool radius compensation.
Contour approach without radius compensation: If you program the
APPR block with R0, the TNC will calculate the tool path for a tool
radius of 0 mm and a radius compensation RR! The radius
compensation is necessary to set the direction of contour approach
and departure in the APPR/DEP LN and APPR/DEP CT functions.
Abbreviation Meaning
APPR Approach
DEP Departure
L Line
C Circle
T Tangential (smooth connection)
N Normal (perpendicular)